Generally, the computer numerical controlled machine tool automatically processes a work piece by using a computer after confirming the position of a cutting tool on a basis of a pre-programmed process condition such as a target processing measurement, a desired shape, a transferring speed of the cutting tool, etc.
FIG. 1 shows the conventional computer numerical controlled lathe 10. Referring to FIG. 1, the computer numerical controlled lathe 10 comprises a frame 12 including a bed 12a, a headstock 14 for grasping and fixing one end of the work piece, which is fixed at one side of the frame 12, a tailstock 16 for grasping and fixing the other end of the work piece, which is sliderably positioned on the bed 12a in opposite to the headstock 14, a tool rest 18 for processing the work piece rotated between the headstock 14 and the tailstock 16 while moving along the longitudinal axis of the bed 12a on she side portion of the bed 12a of the frame 12, a control part (not shown) for controlling the headstock 14, the tailstock 16 and the tool rest 18.
The work piece, which is supported and rotated between the headstock 14 and the tailstock 16, is automatically processed by the cutting tool mounted to the tool rest 18 sliding on the bed 12a on a basis of the pre-programmed process condition.
However, problems with the conventional computer numerical controlled machine tool as described above are that a cutting edge of the cutting tool for processing the work piece may be worn due to the friction between the cutting edge and the work piece and the processing precision of the cutting tool may deteriorate due to the change of the cutting tool's position.
A variety of endeavors for solving these problems have been proposed. One approach, a program for compensating the cutting tool's position so as to compensate a positional deviation between the coordinates of the cutting tool for processing the work piece and the standard coordinates in order to enhance the processing capability of the cutting tool during operation of processing the work piece, has been proposed. This program is preliminarily input to the computer numerical controlled lathe 10.
Additionally, an apparatus for sensing a position of the cutting tool during operation of the processing the work piece for a limited time is installed at the computer numerical controlled lathe 10.
FIG. 2 shows the apparatus for sensing a position of the cutting tool mounted to the computer numerical controlled machine tool, more particularly shows the state that it is mounted to the headstock of the computer numerical controlled machine tool.
As shown in FIG. 2, the apparatus 20 for sensing a position of the cutting tool comprises an arm 22 having a sensor 22a for sensing the position of the cutting tool, a gear assembly 24 for pivoting the arm 22 toward the cutting tool, and a driving motor (not shown) for driving the gear assembly 24.
At the apparatus 20 for sensing a position of the cutting tool, the arm 22 having the sensor 22a is moved toward the cutting tool by means of the gear assembly 24 and then the sensor 22a senses a position of the front end of the cutting tool. Thereafter, the sensor 22a provides the control part of the computer numerical controlled machine tool with a detected value.
The control part of the computer numerical controlled machine tool compares the detected value input from the apparatus 20 for sensing a position of the cutting tool with a standard value, and then calculates a displacement of the cutting tool and it sends a control signal for compensating the position of the cutting tool to the computer numerical controlled machine tool in accordance with the result.
Accordingly, it is possible to compensating the position of the cutting tool to its initial state preliminarily set into the computer.
However, one problem with the apparatus for sensing a position of the cutting tool as described above is that the arm having the sensor must be maintained at a sensing position until the sensor senses the position of the cutting tool. Therefore, the driving motor must be continuously operated and thereby it may be damaged due to the overload applied thereto.